The overall objectives of this project are to evaluate intraluminal influences upon enterocyte development in the small intestine. The basic system utilized in these experiments is organ culture of the rabbit jejunum. Sucrase-isomaltase (SI) is the enzyme system that we are specifically evaluating because we and others have documented that 1) zero enzyme activity is present in the crypt zone in the presence of SI antigen and 2) that this enzyme complex can be stimulated by sucrose substrate. Organ cultures from two animal models were proposed to evaluate substrate effect on SI; a) Starved adult rabbits whose enzyme activity was half the value of control animals but returns to normal in 24 hours with sucrose in the media and b) newborn rabbits prior to the development of significant enzyme activity which is stimulated by the addition of sucrose to the media. The following intraluminal factors were proposed to be added to the organ culture media: a) Substrate (sucrose, fructose, glucose) 2) Pancreatic enzymes (trypsin, elastase) and 3) bile salts (taurine and glycine conjugated primary bile salts.) Finally, utilizing antibody we prepared against pure rabbit SI and its subunits, it was proposed to evaluate the changes in SI antigenicity and activity in the above models in regards to 1) the crypt and along the villus and 2) cytosol and brush border, at timed intervals over a 24 hour period.